1. Field of the Invention
This invention relates to the fabrication of capacitors. More specifically this invention relates to the architecture and method of fabricating ceramic dielectric sheets or ceramic dielectric film on metal foils (film-on-foils), to prepare multilayer capacitors for electronic applications.
2. Background of the Invention
Applications of electronics continues to explode in new areas. Miniaturization is key in some applications, such as in the fabrication of printed circuit boards. The implementation of microelectronics (with power requirements in the nanowatt range, i.e. approximately five (5) nanowatts or lower) and the implementation of power electronic devices (for example, electric vehicle propulsion systems which range from 30-60 kW) are also gaining in popularity. For example, Hybrid Electric Vehicles (HEVs), Plug-In Hybrid Electric Vehicles (PHEVs), military applications all require high power applications and management but in small packages.
Capacitors are integral parts of power electronic devices. For example, capacitors comprise about 35 volume percent, about 25 weight percent, and about 25 percent of the cost of a power inverter in electric drive vehicles.
Performances and life-cycles of these capacitors degrade rapidly with increasing temperature. Separate cooling systems are therefore required to protect inverter units, and these systems add to the costs of the entire machinery. For example, the inverter in the Toyota Prius (2004-2006 model) has a bank of three capacitors, each the size of a soft-drink can, with each capacitor rated at 85° C. and 450 volts, providing 2700 micro farads (μF) of capacitance.
There are fixed capacitors and variable capacitors. Variable capacitors often are made of interleaved plates, one immobile and the other attached to a shaft. Rotating the shaft effectively changes the area of the plates, thus changing the capacitance. Problems with such variable capacitors is that their moving parts make them less robust than their more static monolithic counterparts. Conversely, the problem with fixed capacitors is that their capacitance cannot be varied.
A need exists in the art for a capacitor which will satisfy the requirements of miniaturized electronic systems and high power electronic systems. The capacitor should accommodate different power levels simultaneously, and have a low profile so as to be embeddable into a printed circuit board. The capacitor should also withstand a wide temperature change of operation. New capacitors should free up surface space, increase device reliability, and minimize electromagnetic interference and inductance loss.